Portable microphone and amplifier



' Dec. 14, 1943. w, A, ZARTH 2,336,828

PORTABLE MICROPHONE AND AMPLIFIER Filed Feb. 11,1941 2 Sheets-Sheet 1 INVENTOR William H. 207/};

ATTORNEY Dec. 14, 1943. w. A. ZARTH 2,336,828

PORTABLE MICROPHONE AND AMPLIFIER Filed Feb. 11, 1941 2 sheets-sheet 2 INVENTOR I imam A. 2477/11 Patented Dec. 14, 1 943 PORTABLE MICROPHONE AMPLIFIER William A. Zarth, East Orange, N. J., assignor to Dictograph Products Company, Inc.,'

New

York, N. Y.', a corporation of Delaware Application February 11, 1941, Serial No. 378,328 7 '21 Claims.

This invention relates to telephony and relates more particularly to combined microphones and amplifiers Of a compact type which renders them' suitable for use in hearing aid devices and other small portable telephone systems.

In accordance with the invention, I have provided a small self-contained microphone and amplifier system which may be readily carried about from place to place and, in conjunction with a suitable pocket size power supply and receivers is particularly useful in hearing aid systems.

Preferably, the microphone is of the crystaltype and is combined with a vacuum-tube type of amplifier which includes tubes of such size that they may be disposed in the same casing with the microphone together with the necessary transformers, choke condenser and the like, to mal re a completely self-contained construction which may be readily carried in the pocket or suspended by a clip from, for example, the vest or coat of the individual using the same.

The device, in accordance with the invention, is substantially the same in size as the conventional microphone alone that is used with such hearing aid devices, and therefore, is no more conspicuous or unwieldly than such conventional microphones, and at the same time, ha a gain which is far greater than that of the so-called mechanical amplifiers which are commonly used with portable hearing aid devices.

For a better understanding of the present invention, reference may be had to the accompanying drawings in which:

Fig. 1 is a view in front elevation of a typical form of the microphone amplifier embodying the invention;

Fig. 2 is a view in front elevation of the device in Fig. 1, shown with the front section of the casing thereof removed;

Fig. 3 is a view in section of the device taken on line 3-3 of Fig. 2; and

Figs. 4 and 5 are a diagrammatic showing of typical amplifier circuits used in the device.

As best shown in Fig. 1, the preferred form of the device is provided with a fiat generally tear-drop shape of casing II] which is provided with a grille opening I l in front of the microphone diaphragm l2, best shown in Fig. 1. The casing I0 is preferably formed in two parts, the front section l3 of which is removable in order to expose the microphone and the various elements forming the amplifier for the device.

As shown. in Fig. 2, the microphone diaphragm H which is of the conical type is mounted in the upper center of the casing and, as shown in Fig. 3,

has its edge supported by suitable brackets Mon the back section of the casing l5.

The center of the diaphragm i2 is connected to one corner of the crystal 16 which is fixed to the back casingsection l5, so that upon vibration of the diaphragm in response to voice waves, the crystal will be subjected to a twisting movement which causes the generation of a signal voltage. I I

The two tubes H and I8 of the amplifier which are of thenew small peanut type, and in the preferred form of the. invention may be the CK501 and CK503 pentode tubes, are also mounted in thecasing section 15 and are disposed partially behind the edge of the microphone diaphragm I2 in order to conserve space. The tubes l1 and I8are retained in the casing by means of small C-shaped clips l9 and 20 which may be secured to the section 15 in any desired way, such as, for example, by screws 2|.

The screws 2| also support a combined switch and rheostat element 22 which consists essentially of a strip of insulating material 23 having a resistance coil 24 with which a slider 25 may be brought into engagement. The slider has two resilient fingers 21 and 26, the former engaging the coil 24 and the latter engaging a metallic strip 28 mounted behind the coil 24 to complete the circuit between the batteries, not shown, and

the remainder of the circuit. The slider 25 is terial on which are mounted a choke coil 32 and a transformer 33, these elements being connected by suitable wiring to the remainder of the elements, as will be presently described.

The supporting plate 3! is detachably connected to the casing section l5 to facilitate assembly and repair, if required. The section I5 is also provided with a plurality of jack sockets 34 which are suitably connected in the circuit so that the batteries and the receiver may be readily connected to and disconnected from the microphone and amplifier. 1

Any suitable type of amplifier circuit may be used in the device and I have found that the circuits disclosed in Figs. 4 and 5 are entirely satisfactory. The amplifier circuits may, as

shown in Figs. 4 and 5, be of the impedance coupled type in which the microphone crystal I6 is connected between the filament 35 and the grid 36 of the tube IT. The output from the plate 3| is fed to the choke. or impedance 32 and through a biocking condenser 31 to the grid 38 of the tube IS. The plate 39 of the tube I8 is coupled through the transformer 33 to th receiver 40 which is shown diagrammatically.

The circuit disclosed in Fig. 5 differs from that disclosed in Fig. 4 in that it includes a condenser 4| which is connected in parallel with the choke 32 to permit tuning of the circuit and the elimi ination of unwanted frequencies.

' The voltage output of the amplifiers is controlled by means of the combined switch and rheostat Or voltage control 22 which by variation in the amount of the resistance interposed in the filament circuit of the tubes l1 and I8 varies the filament voltage supplied to the tubes l1 and l 8.

The device preferably is provided with some I means for attaching it to the vest Lorr coat of the user, such as, for example, the spring urged clip element 42 which is fixed to the back of the casing section l5, thereby permitting it to be suspended, for example, from "the vest pocket or outer coat pocket of the wearer.

From the foregoing description of a typical vform of combined microphone and vacuum tube amplifier it will be apparent that I hav provided an efiicient yet extremely compact construetion which eliminates the need of a separate amplifier system.

The device permits the frequency response of the'microphone andthe receiver to be varied to produce'the most suitable frequencies to complement the defective hearing of the user and,

7 ing said transformer and be used in such circuits with equal facility, so long as the device is of a compact natur and is readily portable. Therefore, the form of the invention described above should be considered as illustrative and not as limiting the scope of the following claims. I

I claim:

1. A portable microphone and amplifier for hearing aid devices comprising a casing having a grille adjacent one end thereof, means for suspending the casing from the clothing of the user,

a crystal microphone secured to the back of said casing having a diaphragm disposed within said casing behind said grille, an impedance coupled amplifier including miniature vacuum tubes, a transformer and a choke within said casing, means for securing said tubes at least in part behind said diaphragm, a series of jacket sockets in another end of said casing, a sub-panel extending from adjacent to said jack sockets to adjacent the diaphragm, said sub-panel supportsaid choke, a combined switch and volume control in said one end of said casing and a circuit connecting said microphone, amplifier, jack sockets and switch and volume control, whereby said microphone and amplifier may be connected to an independently supported source of electrical energy anda receiver.

2. Aportable microphone and amplifier unit for hearing aid devices comprising a casing of relatively fiat form adapted to be worn by a user,

said casing having a back with means thereon for attaching the casing to the user's clothing, a microphone located within the casing and including a conical diaphragm facing toward the front of the 'casing, vacuum tubes located in said casing and disposed adjacent the marginal portions of said diaphragm and between said portions and the back of the casing, a sub-panel located in said casing beside said diaphragm and parallel to the back thereof and supporting a, choke coil and transformer and means on said casing for electrically connecting said sub-panel and the elements supported thereby to an independently supported source of energy and a. receiver.

. W. A. ZARTH. 

